Semiconductor fabrication typically involves applying several different processes to a semiconductor wafer at different times during the manufacturing process. Most of these processes involve the application of gas and/or plasma to the wafer while the wafer is positioned on a pedestal in a processing chamber of a processing machine or device. In some instances, a processing device will have more than one pedestal to allow multiple wafers to be processed simultaneously. Simultaneous processing of wafers increases the production rate of wafers resulting in higher profits and faster production.
Many modern processing devices make use of an optical spectrometer in controlling the process in the chamber. Optical emission spectroscopy (OES) involves the use of the optical spectrometer to monitor the intensity of one or more selected wavelengths of the plasma in the chamber for changes during the process. The intensity of the wavelength is plotted over time as a process endpoint signal which provides a convenient way to track changes in the selected wavelength. Certain changes in the intensity are used to identify when the process is completed. For instance, in some cases when a photoresist stripping or ashing process is completed there is a distinct drop in the amplitude of the endpoint signal corresponding to a drop in the intensity of the wavelength when the process is completed.
It has been recognized that in order to ensure optimum plasma uniformity and heat transfer profile on the wafer, the wafer must be properly positioned on the pedestal. When the wafer is not properly positioned on the pedestal, there is an increased incidence of defects in the wafer resulting from the process. One such position is when the wafer is tilted with respect to the way in which the wafer is designed to sit on the pedestal. In the tilted orientation one side of the wafer is separated from contact with the pedestal. One cause of the wafer assuming the tilted orientation is the result of a stray piece of material accidentally becoming positioned between the wafer and the pedestal. Another cause can be if the pedestal or other part of the processing device becomes loose or detached in the processing device such as loose or stuck lift pins. Other causes can also result in the wafer not being properly positioned during the application of the process.
Problems relating to the improperly positioned wafer can arise in some instances where the pedestal serves to heat the wafer during the process. A slight variation in the horizontal arrangement or tilt of the wafer with respect to the pedestal in these and other circumstances can result in an increased number of wafer defects, thereby reducing yield and increasing production costs.
Visual inspection of each wafer as it is placed on the pedestal can determine if the wafer is tilted. Many processing devices have inspection windows which allow for the observation of the wafer in the processing chamber. However, this manual approach is cumbersome and costly and may not be practical for other reasons related to the frequency in which these problems arise.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon reading of the specification and a study of the drawings.